For those of you who just wants to compare the comic to the movie, or download the original story quick and easy, here's a torrent containing Frank Miller's Sin City and CDisplay Comic Book Reader for easy viewing.
I've read Sin City a few years back when I borrowed it from the local library, and I must say it's an old favourite. Not recommended for the weak-hearted though, it contains lots of violence and gore (even though it's b/w).
Have a nice time reading!